Dave Shrader wrote:
. . .
A major point of caution is required. The NEC requires ONLY ONE ground
connection. Multiple ground connections introduce VERY SERIOUS ground
loops that may violate the NEC criteria. This opens a VERY LARGE loop
hole in your home owner's insurance policy. If you are adding a second
earth [ground] connection at your station use an isolation transformer
to break up the ground loops in the basic 120 VAC connection. Consult
with an electrician regarding your local and NEC codes.
. . .

My NEC book is getting pretty old now, 1990, but at that time, multiple
grounds were often not only permitted, but required. And a *minimum*
spacing was sometimes specified.

For example, section 250-84, Resistance of Made Electrodes: "A single
electrode consisting of a rod, pipe, or plate which does not have a
resistance to ground of 25 ohms or less shall be augmented by one
additional electrode of any of the types specified in Sections 250-81 or
250-83. Where multiple rod, pipe, or plate electrodes are installed to
meet the requirements of this section, they shall be not less than 6
feet (1.83m) apart."

Or section 250-81(a), Metal Underground Water Pipe: ". . .A metal
underground water pipe shall be supplemented by an additional electrode
of a type specified in Section 250-81 or in Section 250-83. The
supplemental electrode shall be permitted to be bonded to the grounding
electrode conductor, the grounded service-entrance conductor, the
grounded service raceway, any grounded sevice enclosure, or the interior
metal water piping at any convenient point."

When I replaced the service (in 1979) in my 1952 house, the system
ground was a water pipe connection and I was required to add a ground
rod. Neither was considered adequate in itself; both were required by
the code at that time.

I agree wholeheartedly about consulting an electrician. Non-electricians
(including me) often have mistaken ideas about the content of the NEC.
It doesn't hurt to have an up to date copy of the NEC for reference,
either, if you anticipate doing any of the work yourself.

Roy Lewallen, W7EL